In recent years, switch devices such as pressure switches, proximity switches, photoelectric switches, etc. have a tendency to perform multiple functions, including additional functions such as trouble precognition and an analog output functions, etc. as well as merely performing a signal on/off output function. Further, setting sections and displays or the like corresponding to the respective switch devices become complicated as the demand for multiple functions increases, as compared with the devices employed in the prior art.
A pressure switch according to the prior art will now be shown in FIG. 1 as an illustrative example.
The pressure switch 1 has a display 3 for displaying a pressure thereon, which is provided on an upper surface of a body 2 shaped substantially in the form of a rectangular parallelopiped. A pressure setting screw 4 formed of a minus screw, and an operation indicator or operation pilot lamp 5 for indicating the state of operation of the pressure switch 1, are disposed adjacent to the display 3. A desired pressure value is set by turning the pressure setting screw 4. For example, a semiconductor pressure sensor (not shown) is incorporated in the body 2 to detect the pressure of air introduced from an opened pressurized air introduction port 6, and for converting the pressure into an electric signal. Further, a conductor unit 7 is provided extending from one surface of the body 2, which is opposite to the pressurized air introduction port 6, to drive the semiconductor pressure sensor and supply a detected signal to an unillustrated external fluid device. A cylindrical member 8 having a pressurized air introduction port 6 opened at its tip portion is integrally connected to a lower portion of the body 2. A male screw 9 for connecting and fixing the cylindrical member 8 to another device is formed on the outer periphery of the cylindrical member 8, and permits the cylindrical member 8 to communicate with a fluid passage through which the pressurized air flows.
However, a setting section comprised of the display 3 and the pressure setting screw 4 or the like is not always necessary for the pressure switch 1 according to the prior art. The setting section is merely used to confirm and adjust a preset pressure to be used when the pressure is set in advance, or when troubles such as an excessive pressure, overcurrent, etc. have occurred, or merely used for maintenance and inspection of the pressure switch 1.
Further, recent control devices have an increased capacity for so-called artificial intelligence. It is thus necessary to provide power lines, control signal lines or a number of various conductors or wires between the control devices and sensors for the purpose of communication or the like. Further, the sensors for detecting various control states of the signal lines used for controlling the control devices, or those of the control devices, need power sources for driving circuits in addition to the signal lines.
When a transistor is used for driving a sensor, for example, it is necessary to provide a ground line, a power line and a signal line when using either PNP or NPN type transistors. In the case of each control device, on the other hand, it is necessary to provide, for example, wires for activating the drivers used for actuators including fluid pressure and electrical operations, a power line or a power line or the like used for a control circuit.
However, inconvenience or undesired troubles are developed in that when the signal line, the ground line and the power line are respectively provided in a separate manner, the wiring structure becomes complicated. Further, when the signal line, the power line, etc. are collectively wired, they interfere with each other so as to produce noise, and hence a desired control cannot be performed. Further, a drawback also arises in that miswiring can result during wiring.